1. Field of the Invention
The present invention is directed to an arrangement for avoiding unwanted degradation in no-load operation of, in particular, solar cells composed of amorphous silicon, the solar cells being interconnected in modules.
2. Description of the Prior Art
Solar cells can be particularly advantageously employed where little maintenance for systems or devices is possible or other electrical energy sources are not available. The latter is particularly true for the use of small appliances for mobile homes, sail boats, mountain chalets and the like.
Recently, amorphous silicon solar cells have gained increasing significance. In comparison to crystalline silicon solar cells, amorphous silicon solar cells have the advantage of less expensive manufacture as a result of their thin-film structure. The stability of solar cells of amorphous silicon, however, causes problems whose elimination has become the subject matter of many investigations. Therefore, for example, a report of M. Moeller et al in the conference of the Materials Research Society Symposiums, Vol. 49, 1985, pp. 325-330 discloses that the stability behavior of amorphous silicon solar cells can be improved in that, given p-i-n solar cells having a transparent base electrode composed of doped tin oxide, a boron doping profile decreasing in the direction of the i-n junction, be incorporated into the i layer when the light incidence occurs from the n side or that, given irradiation from the p side, the i layer contains a phosphorous doping profile which increases in the direction of the i-n junction.
The measures discussed above also lead to solar cells or, respectively, solar cell modules in which a considerable aging occurs under load, i.e. given a connected load, than in no-load operation of the module. This is particularly the case with modules having efficiencies above 5% that are manufactured with the cell type glass substrate/tin oxide as a base electrode/p-SiC-i-n as a thin film/metal as a rear electrode.
Given suitable manufacture, the degradation of these modules after an initial aging of a few percent can be extremely low, for example, less than 10% after ten years operation in sunlight when they are continuously operated under load. Operation under no-load conditions, by contrast, can lead to the doubling of the degradation. The no-load conditions occur when the module is mistakenly not connected to the load or when the load, despite a cable connection, is separated from the module either intentionally or unintentionally, for example given a cable malfunction. The end effect in any case, however, is a premature, unnoticed decrease of the module power caused by the degradation.